1. Field of the Invention
The present invention relates generally to head mounted displays and more particularly to adjustment mechanisms for controlling the alignment of the head mounted displays with a wearer's eyes.
2. Description of the Related Art
Head mounted displays have been used for years in a number of applications as a replacement for the conventional cathode-ray-tube (CRT) and liquid-crystal flat panel displays. Head mounted displays have been used, for example, in 3-D applications, video game applications, virtual reality applications, military applications, and other applications where mobility or privacy are desirable.
Traditionally, head mounted displays have been either mounted to helmets worn by the user, or incorporated mechanisms that used a compression fit against the head to keep the display in place. One examples of such a mechanism is shown in U.S. Pat. No. 5,739,893, entitled "Head-Mounted Image Display Apparatus." This mechanism controls the position of the head mounted display by adjusting the compression between a pad pressing against the back of the head and a pad that rests on the forehead. A similar mechanism is shown in U.S. Pat. No. 5,812,224 entitled, "Head-Mount Image display Apparatus" in which the pads at the back of the head are spring loaded to control the pressure.
Another example of a compression fit mechanism is shown in U.S. Pat. No. 5,757,339, entitled "Head Mounted Display." This mechanism allows a wearer to adjust the position of the display by controlling the circumference of a padded headband. A similar headband mechanism is depicted in U.S. Pat. No. 5,774,096, entitled "Head Mounted Display." These mechanisms give the wearer some ability to adjust the height of the display relative to the eye.
Recently, some head mounted displays have been developed that are worn more like eyeglasses (eyeglass displays). These eyeglass displays support the entire weight of the head mounted display on the wearer's ears and nose. Thus, if the position of the eyeglass displays on the face is to be adjusted, the adjustment should occur either between the ear contacts and the "rims" of the eyeglass display, or between the nose contact and "bridge" located between the rims of the eyeglass display.
Eyeglass displays having a nose bridge 1 that can be adjusted in and out to control the distance between the wearer's eyes and the video display portions 2 of the eyeglass displays are shown in FIG. 1 and described in U.S. Pat. No. 5,815,126, entitled "Monocular Portable Communication and Display System." This adjustable nose bridge allows the wearer to select the optimal viewing distance between the eye and the display portion of the eyeglass display despite variations in the wearer's facial structure and vision. The eyeglass display shown in FIG. 1, however, lack a nose bridge that can adjust to accommodate variations in height and tilt that might be desired by the wearer.
Height adjustment for eyeglasses, on the other hand, have been considered in the past. For example, controlling the height of bifocal eyeglasses using an adjustable nose bridge is shown in FIG. 2A and FIG. 2B and additionally described in U.S. Pat. No. 4,280,758. Adjusting the height of bifocals allows the wearer to position the lower (reading) lenses 3 of the bifocal glasses 4 where they are most convenient for the task at hand. Thus, when reading a book on a table a wearer might prefer the reading lenses low so she could conveniently look down through the reading lenses at the book without having to tilt her head down in an exaggerated way to interpose the reading lenses between her eyes and the book. At the same time, the lowered reading lenses allow the wearer to look forward through the upper (long distance) lenses 5 at her surroundings. Alternatively, a wearer using a computer might prefer the reading lenses 3 raised in order to view a computer screen through the reading lenses without tilting her head back to interpose the reading lenses between her eyes and the computer screen.
Adjusting the height of an eyeglass display may also offer certain advantages. For example, wearing an eyeglass display low on the face would allow the wearer to make eye contact with another person while conversing. At the same time, the lowered eyeglass display could allow the wearer to glance down and view data relevant to the conversation displayed on the eyeglass display. Alternatively, the lowered eyeglasses may be preferred by a wearer who spends a great deal of time viewing data through the displays so that she may remain aware of her surroundings by looking over the top of the eyeglass display.
Similarly, a wearer might choose to wear the eyeglass display high on the face. This configuration might be convenient for those who work with their hands and follow complex procedures such as doctors or mechanics. The raised eyeglass display may be used, for example, to show instructions, diagrams, or alternate views of the subject to the wearer. At the same time, the wearer's hands, any instruments or tools, and the subject of the instructions are in full view below the eyeglass display.
Finally, despite the advantages discussed above of wearing the eyeglass display high or low on the face, some wearers will undoubtedly prefer to wear the eyeglass display at eye level on the face. This position would be the most distraction free and thus it might be preferred for viewing a movie, enjoying a virtual reality experience, or simply concentrating on important work.
Merely raising and lower the eyeglass display on the face using a mechanism similar to that shown in FIG. 2A and FIG. 2B, however, will not allow the most efficient viewing of the eyeglass display by the wearer. This is because the images displayed within the eyeglass display are typically configured to be viewed optimally when the wearer's line of sight is perpendicular to the plane of the image. Usually, the eyeglass display is configured so that the perpendicular viewing angle is achieved when the eyeglass display is worn at eye level. When the height of the eyeglass display on the face is controlled using a nose bridge that merely raises or lowers, however, the eyeglass display will pivot about the wearer's ears as the height of the eyeglass display is adjusted. Since the wearer's ears rather than the wearer's eyes act as the pivot, the wearer's viewing angle will not remain perpendicular to the plane of the displayed image when the display is moved above or below eye level. To compensate for the change in viewing angle that occurs when the height of the eyeglass display on the face is changed, the eyeglass displays should include an adjustment for tilt. The tilt adjustment would allow the optimal perpendicular viewing angle to be achieved at whatever height the wearer chooses to wear the eyeglass display.
From the foregoing it will be apparent that there is a need for a nose bridge for an eyeglass display which can be used to adjust the height of the display on the face, the tilt of the display, and the distance between the eye and the display.